You have to edit the tag you want to color. Add |cffRGB in front of the tag. R,G and B stand for red, green and blue. Each is a number in the hexadecimal system in the range from 00 to FF. The higher the value the brighter the color. See Wikipedia on how the RGB system works.

so Aviana, do you know how to change the colors of texts on unitframes with the color codes?
I need green and blue for Health and Mana, any help would be really awesome, but try to maintain the Addon's functionality as the first prio :)

If you want your old settings got to
..\World of Warcraft\WTF\Account\ACCOUNTNAME\SavedVariables
and rename ShadowedUnitFrames.lua to SimplisticUnitFrames.lua then open it and replace ShadowedUFDB with SimplisticUFDB.

If you use this and have character wich uses one of the new bars (holy power, soul shards etc) you will get errors.